Anti-reflective coatings for optically transparent substrates

ABSTRACT

Anti-reflective coatings and coating solutions, optically transparent elements and improved processes for preparing AR coatings and coating solutions are described. The anti-reflective coatings are formed from at least two different alkoxy silane materials in a base catalyzed reaction.

RELATED APPLICATION

This application claims the benefit under 35 U.S.C. §119(e) of U.S.Provisional Application Ser. No. 61/268,231, entitled “ANTI-REFLECTIVECOATINGS FOR SOLAR MODULE GLASS AND SOLAR CELLS AND LENSES”, filed Jun.10, 2009. This application is incorporated by reference herein in itsentirety.

TECHNICAL FIELD

The invention relates generally to anti-reflective coatings foroptically transparent elements and more particularly to anti-reflectivecoatings for glass covers used in photovoltaic cell applications.

BACKGROUND

Anti-reflective (AR) coatings are used in several industries, includingin the manufacture of photovoltaic (PV) modules, to reduce thereflection fraction of incident light as light passes through anoptically transparent element such as glass. The goal of AR coatings isto achieve a refractive index that is as close to 1.23 as possible tomaximize light transmission over a broad band of light wavelengths.

One or more layers of a low refractive index coating can achieveimproved transmittance in a broad wavelength range and a wide range ofincident angles. Such coatings can be deposited (at atmospheric pressureor without vacuum) as sol-gel materials and can be highlycost-effective. These thin anti-reflective coatings, which may be formedfrom a silicon dioxide sol-gel applied to the glass cover byconventional coating techniques, have been reported to improve solarlight transmittance by about two to three percent in the visible portionof the light spectrum. Such sol-gels have been formed using severalmechanisms including via hydrolysis/condensation reaction of alkoxysilanes. See, e.g., G. Wu et al., “A novel route to control refractiveindex of sol-gel derived nanoporous films used as broadbandantireflective coatings,” Materials Science and Engineering B78 (2000),pp. 135-139. However, AR coatings formed from silicon dioxide coatingswould benefit from improved hardness, adhesion, shelf-life and/orprocessing efficiency.

SUMMARY

Embodiments disclosed herein pertain to AR coatings and coatingsolutions, optically sensitive elements such as photovoltaic modulesthat employ AR coatings, and improved processes for preparing ARcoatings and coating solutions.

One embodiment is an optically transparent element including anoptically transparent substrate and an AR coating disposed on at leastone surface of the optically transparent substrate. The AR coatingincludes a polymer having at least one tetraalkoxy silane residue and asecond alkoxy silane residue. The at least one tetraalkoxy silaneresidue may include tetraethoxy silane. The second alkoxy silane residuemay include triethoxysilanes such as methyltriethoxy silane andvinyltriethoxy silane, diethoxy silanes such as dimethyldiethoxy silaneand methyldiethoxy silane and/or combinations of the foregoing. Thepolymer may further include metal alkoxide residues such as titaniumisopropoxide. The polymer contained in the AR coating may comprisepolymer particles having an average size of no more than 100 nm. Anotherembodiment is a photovoltaic module including at least one opticallytransparent element described above.

Another embodiment also provides a method of producing an AR coatingsolution in which at least two alkoxy silane materials as describedabove are combined in a solvent with a base catalyst under suitablereaction conditions to form an AR coating solution. The pH of the ARcoating solution is then reduced, and the resulting average polymerparticle size in the AR coating solution is between about 15 nm andabout 100 nm. A further embodiment is a method of forming an opticallytransparent element by dispensing the AR coating solution onto anoptically transparent substrate and curing.

A further embodiment provides an AR coating solution including a polymerhaving residues of tetraethoxy silane, methyltriethoxy silane and/orvinyltriethoxy silane. The AR coating solution has a pH of less than 5and a viscosity of less than 2 cP. The pH and viscosity of the ARcoating solution are stable for at least 24 hours at room temperature.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a flow chart of a method of producing an optically transparentelement including an AR coating in accordance with an embodiment of theinvention.

FIG. 2 provides a schematic illustration of a photovoltaic cellincluding an AR coating in accordance with an embodiment of theinvention.

FIG. 3 is a schematic illustration of a portion of a polymer molecule inaccordance with one embodiment of the present invention.

DETAILED DESCRIPTION

FIG. 1 is a flow chart illustrating a method 10 of forming an AR coatingsolution and optically transparent element according to one embodiment.According to the method 10, an AR coating solution is formed bycombining at least two different alkoxy silane materials in a solventand in the presence of a base catalyst under suitable reactionconditions to cause polymerization of the alkoxy silane materials (Block20). The resulting AR coating solution includes a polymer having atleast two different alkoxy silane residues.

After combining the alkoxy silane materials, an acid may be added to theAR coating solution to adjust the solution pH (Block 30) and/or the ARcoating solution may be further combined with at least one additionalsolvent (Block 40). In one embodiment, exemplary AR coating solutionsare formed without the use of poragens such as polyethylene glycols orpolyethylene oxides that evaporate during thermal processing steps toform pores. Additionally, the AR coating solutions are formed withouthaving to filter the resulting polymer from the reaction solution or toremove components in the solution as required by other reaction methods.

The AR coating solution is dispensed onto an optically transparentsubstrate such as a glass substrate (e.g., sodalime glass, float glass,borosilicate and low iron sodalime glass), plastic cover, acrylicFresnel lense or other optically transparent substrate (Block 50). TheAR coating solution is then cured to form an AR coating on the opticallytransparent substrate (Block 60).

A variety of commercially available alkoxy silanes may be used to formthe AR coating solution. Suitable alkoxy silanes that comprise the firstof the at least two alkoxy silane materials include tetraalkoxy silanes,which may include one or more ethoxy, methoxy, and/or propoxy groups aswell as hydrogen, methyl, ethyl or propyl groups. In one embodiment, atleast one of the alkoxy silane materials is tetraethoxy silane (TEOS).

A second alkoxy silane material may be added to promote improved ARcoating adhesion and/or other improved coating properties. Examples ofthese materials include trialkoxy silanes such as methyltriethoxy silane(MTEOS), aminopropyltriethoxy silane (APTEOS) and APTEOS-triflate,vinyltriethoxy silane (VTEOS), and diethylphosphatoethyltriethoxysilane. Examples also include dialkoxy silanes such as methyldiethoxysilane (MDEOS) dimethyldiethoxy silane (DMDEOS), and phenyldiethoxysilane (PDEOS). Suitable monoalkoxy silanes include trimethoxy silanessuch as (3-glycidoxypropyl)-trimethoxy silane. Carbosilanes, mercaptosilanes, hydridosilanes and silazanes such as dimethyldisilazane mayalso be suitable. Combinations of these second alkoxy silane materialsmay also be used. For example, MTEOS and/or VTEOS may be particularlysuitable for improving adhesion and/or hardness. In one embodiment, thesecond alkoxy silane material or combination of materials may becombined with the first alkoxy silane material in an amount ranging fromup to about 50 mol % to 40 mol % to 35 mol % to 25 mol % to 15 mol %based on the total moles of alkoxy silane material. In anotherembodiment, the second alkoxy silane material may be added in an amountranging from at least about 10 mol % to at least about 40 mol % based onthe total moles of both alkoxy silane materials. The molar ratio of thefirst alkoxy silane to the second alkoxy silane material may range from1:1 to 1000:1, more particularly from 10:1 to 500:1 and even moreparticularly from 25:1 to 100:1.

In addition to the alkoxy silane materials, at least one metal alkoxidemay be included in the AR coating solution. Suitable metal alkoxidesinclude metal isopropoxides and metal butoxides. Examples of metalisopropoxides include zirconium isopropoxide and titanium isopropoxide(TIPO). Examples of suitable metal butoxides include hafnium-n-butoxideand zirconium-n-butoxide. TIPO may be particularly suitable forimproving AR coating hardness. In one embodiment, the AR coatingsolution includes less than 1 mol % metal alkoxide based on the totalmoles of metal alkoxide and alkoxy silane.

Combinations of the foregoing materials may be utilized to achievedesirable coating properties. In one embodiment, the AR coating solutionincludes TEOS and MTEOS. In another embodiment, the AR coating solutionincludes TEOS, MTEOS, VTEOS. In a further embodiment, the AR coatingsolution includes TEOS, MTEOS, VTEOS and TIPO.

Suitable base catalysts added to the AR coating solution include, forexample, quaternary amine compounds of the formula R₁R₂R₃R₄N⁺OH⁻ inwhich R₁, R₂, R₃ and R₄ are each independently phenyl, hydrogen or aC₁₋₁₆ alkyl. In some embodiments, suitable base catalysts includequaternary amine hydroxides such as tetrabutylammonium hydroxide andtetramethylammonium hydroxide. In some embodiments, suitable basecatalysts include aqueous solutions of these components, and mayoptionally include additional distilled water beyond that found in thebase catalyst aqueous solutions.

Examples of suitable solvents or diluents that may be used in the ARcoating solution include but are not limited to acetone, water,propylene glycol methyl ether acetate (PGMEA), isopropyl alcohol (IPA),tetrahydrofuran (THF), ethanol, dipropylene glycol, tetraethyleneglycol, ethyl acetate, PGME and combinations. In some embodiments, thesolvent is free of acetone.

These components may be combined and reacted in, for example, a jacketedstirred tank reactor (STR) via a batch or semi-batch mode for a suitablereaction time in the range of about 1 to about 6 hours, moreparticularly 1 to 3.5 hours and at a suitable temperature in the rangeof about 35° C. to 70° C.

Under the foregoing conditions, a hydrolysis reaction takes place toform a polymer in solution. Depending on the reaction conditions, thepolymer contained in the solution may vary from linear or randomlybranched chains, to porous matrices, to dense colloidal particles. Inany case, the resulting polymer will include residues of at least twodifferent alkoxy silane materials as described above and/or the optionalmetal alkoxide materials. The term “residue” as used herein is intendedto refer to a portion of the polymer molecule derived from the alkoxysilane and/or metal alkoxide materials initially added to the AR coatingsolution. By way of example, it is generally known that tetraethoxysilane reacts under the foregoing conditions to form units of SiO₄,which would constitute one example of a tetraethoxy silane residue. Itwill also be appreciated that certain by-products may be formed andcontained in the AR coating solution either as part of the polymer or asa separate component. For example, the hydrolysis of TEOS may result inthe formation of ethanol as a by-product. FIG. 3 illustrates a depictionof an exemplary polymer molecule portion with certain residues circled.

In any case, the polymer includes at least two different alkoxy silaneresidues derived from the alkoxy silane materials discussed above. Inone embodiment, the polymer includes at least one TEOS residue, at leastone MTEOS residue or both. In another embodiment the polymeradditionally includes at least one VTEOS residue. In a furtherembodiment, the polymer additionally includes at least one TIPO residue.

To further control the reaction conditions, the pH of the AR coatingsolution can be adjusted to between about 0 to about 4.0, moreparticularly, from about 0 to about 2.0 and even more particularly fromabout 0.5 to about 1.7 using an acid such as nitric acid after asuitable reaction time. This pH reduction may affect the polymerizationcondition, which in turn controls the polymer particle size contained inAR coating solution and subsequently cured coating. In one embodiment,the average particle size of the polymer in the AR coating solution maybe less than 10 nm, more particularly, less than 1 nm. The averageparticle size of the AR coating after curing may be between about 15 andabout 100 nm, more particularly, between about 25 and about 75 nm, andthe polymer may have a molecular weight in the range of about 25,000 toabout 150,000 Dalton. The AR coating may also be further diluted with asolvent that includes one or more of water, IPA, acetone and/or PGMEA.Additional acid may be added during dilution to maintain a desired pH.

The AR coating solution may be dispensed onto a surface of an opticallytransparent element by a variety of generally known coating methodsincluding spin-on, slot die, spray, dip, roller and other coatingtechniques. The amount of solvent included in the initial reaction oradded to the AR coating solution may be varied such that the solidsconcentration of the AR coating solution ranges from about 1 to about 25weight percent depending upon the dispensing method. In someembodiments, there may be manufacturing advantages to forming a moreconcentrated batch in the STR, followed by diluting to a desiredconcentration. In alternate embodiments, dilution could occur prior toor during the initial mixing stage. For dip coating, a solidsconcentration of about 10 to 20 weight percent is desired. For othercoating methods such as spin, slot die and spray, a lower solidsconcentration of about 1 to 6 weight percent may be desired. Embodimentsof the present invention may be particularly suitable for sprayapplication due to the relatively small polymer particle size achievableby the manufacturing process described above. The viscosity of theresulting coating solution may vary from between about 0.75 cP to about2.0 cP.

Unlike other methods of forming AR coating materials, the AR coatingsolution of the present invention is ready for use without removing theparticles from solution. Additionally, the AR coating solutions formedby embodiments of the present invention may remain stable for anextended period of time. As used herein, stability refers to the opticaland/or mechanical performance characteristics of the coating solutionincluding, without limitation, light transmittance, viscosity, adhesionand/or pH. At room temperature, coating solutions of the presentinvention may remain stable for at least 24 hours, more particularly,about one week, even more particularly, about 4 weeks. Additionally,coating solutions of the present invention may be stored in a −20° C. to−40° C. freezer for up to at least six months without materiallyimpacting the optical or mechanical properties desired for glasscoatings. The ability to preserve AR coatings for an extended period oftime may provide a significant manufacturing advantage, particularly ifthe coating solution is transported to an off-site location and/orstored for a period of time prior to use.

After application, the AR coating solution is cured onto the opticallytransparent substrate. When applied to glass substrates, the AR coatingsolution can be subjected to a high temperature heat tempering step,ranging from about 600° C. to about 750° C. depending on the glasscomposition, for between about 1 minute and about 1 hour to cure thecoatings. It will be appreciated that the various alkoxysilane and/ormetal alkoxide residues described above may be further modified duringthe curing process. However, these additional derivative residues stillconstitute alkoxysilane and/or metal alkoxide residues for the purposesof the present application.

AR coated optically transparent elements according to embodiments of thepresent invention may possess improved light transmittancecharacteristics. For example, the AR coating may have a refractive indexin the range of about 1.15 to about 1.3, resulting in up to about a 4.26percent transmission gain in the visible portion (350 to 800 nanometers)of the light spectrum and/or up to about a 3 percent transmission gainin the infrared portion (800 to 2500 nanometers) of the light spectrum.

If both sides of an optically transparent substrate are coated, up toabout an 8-9 percent transmission gain in the visible portion of thelight spectrum and up to about a 5-7 percent transmission gain in theinfrared portion of the light spectrum may be obtained. Exemplary datarelating to these properties are presented in the Examples section setforth below. In some embodiments, the absolute gain in transmittance isindependent of the coating methods used as long as the thickness of theAR film is tuned to the incident light wavelength (the AR film thicknessis about ¼th the wavelength of the incident light).

As further demonstrated in the Examples, AR coatings of the presentinvention may also have improved adhesion and/or hardness compared toconventional sol gels. Additionally, AR coatings that include TIPO mayhave self-cleaning properties due to the generation of hydroxyl radicalsin the presence of water and solar UV light. The hydroxyl radicals mayoxidize water insoluble organic dirt on the glass surface to form highlywater-soluble compounds that are washed out during rain. Theself-cleaning properties could be optimized according to the amount ofTIPO added. In some embodiments, a TIPO content of about 0.0005 moles toabout 0.003 moles is exemplary.

FIG. 2 is a cross-sectional view of a photovoltaic module (e.g., solarcell) for converting light to electricity, according to an embodiment ofthis invention. Incoming or incident light from the sun or the like isfirst incident on AR coating 1, passes therethrough and then throughglass substrate 2 and front transparent electrode 3 before reaching thephotovoltaic semiconductor (active film) 4 of the module. The module mayalso include, but does not require, a reflection enhancement oxideand/or EVA film 5, and/or a back metallic contact and/or reflector 6 asshown in FIG. 2. Other types of photovoltaic devices may of course beused, and the FIG. 2 module is merely provided for purposes of exampleand understanding. It will also be understood that a module may includea single AR coated optically transparent substrate that covers multiplephotovoltaic cells connected in series.

As explained above, the AR coating 1 reduces reflections of the incidentlight and permits more light to reach the thin film semiconductor film 4of the photovoltaic module thereby permitting the device to act moreefficiently. While certain of the AR coatings 1 discussed above are usedin the context of the photovoltaic devices/modules, this invention isnot so limited. AR coatings according to this invention may be used inother applications. Also, other layer(s) may be provided on the glasssubstrate under the AR coating so that the AR coating is considereddisposed on the glass substrate even if other layers are providedtherebetween.

EXAMPLES 1-16

In Examples 1-16, 122 grams of isopropanol and 62 grams of acetone werecharged into a reactor. In Examples 1-10, 0.09 moles of tetraethoxysilane (TEOS) and 0.01 moles of methyltriethoxy silane (MTEOS) wereadded to the reactor while stirring with an agitator. In Examples 12-16,the molar ratio of TEOS to MTEOS was varied. The total moles of allmonomers were kept at a constant total of 0.1 moles to simplify kineticsmeasurements. Table 1 below sets forth the specific component amountsused for each Example.

Tetrabutylammonium hydroxide (TBAH) (0.002 moles of 40% aq. solution) ortetramethylammonium hydroxide (TMAH) (0.002 moles of 25% aq. solution)was added as a base catalyst and the reaction mixture was then heated to35-70° C. for 1-3.5 h. The reaction mixture was then cooled and nitricacid was added to the reaction mixture in a semi-batch fashion to adjustthe pH of the reaction mixture to 0.5-1.7. The reaction mixture was thencooled and diluted with IPA, Acetone and/or PGMEA. The molecular weightwas measured by Gel permeation chromatography and it ranged from about25,000-150,000 Dalton depending on reaction conditions. After dilutionand pH control the polymer formulation was stored in a −20° C. to −40°C. freezer.

After storing in a frozen state, these formulations were then depositedon glass or transparent substrates. Dip, slot, die, roller and spincoating techniques were attempted. In almost all cases the desiredcoating thicknesses of 125 nm was obtained by curing at 200-700° C.,more favorably at 600-750° C., in air or nitrogen after 3 minutes to 1hour. A broadband spectroscopy tool available from n&k Technology, Inc.was used for coating thickness measurements. Average polymer particlesize in the coating was determined to be between 10 and 100 nm by SEManalysis.

Transmittance data were measured by UV-Visible spectral measurement thatmeasures wavelengths from 300-2500 nm. A broadband spectroscopy toolavailable from n&k Technology, Inc. was used for refractive indexmeasurements. Tables 1 and 2 provide composition and performance datafor Examples 1-16.

A Pencil Hardness test was used as an indicator of scratchresistance/hardness and was performed by attempting to scratch the ARcoating with pencils of various hardness (e.g., 3B, 4B, etc.). AnAdhesion Tape Test was used as an indicator of coating adhesion and wasperformed by forming cross-hatches in the coating, pressing anadhesive-backed tape material to the coated substrate, pulling the tapeaway from the coating and then studying the effect the tape had on thecross-hatched portions of the coating. A Contact Angle Test was used todetermine the contact angle of the AR coated substrate using a VCA 2500instrument available from AST Products, Inc. The results of these testsare shown in Table 2.

TABLE ONE Mole Mole Mole Mole Reaction Example TEOS MTEOS TBAH TMAH Time(h) 1 0.09 0.01 0.0005 0 3.5 2 0.09 0.01 0.001 0 3.5 3 0.09 0.01 0.002 03.5 4 0.09 0.01 0.004 0 2.5 5 0.09 0.01 0.005 0 2 6 0.09 0.01 0.007 0Gelled 7 0.09 0.01 0 0.0005 3.5 8 0.09 0.01 0 0.001 3.5 9 0.09 0.01 00.002 2.5 10 0.09 0.01 0 0.003 Gelled 11 0.09 0.01 0.002 0 3.5 12 0.080.02 0.002 0 3.5 13 0.07 0.03 0.002 0 3.5 14 0.06 0.04 0.002 0 3.5 150.05 0.05 0.002 0 3.5 16 0.064 0.036 0.002 0 3.5

TABLE TWO RI at % T Pencil Adhesion Thickness 550 Gain at Hard- TapeContact Example (nm) nm 550 nm ness Test Angle 1 125 1.2 4 3B Poor <10 2125 1.2 4 3B Poor <10 3 125 1.19 4 3B Acceptable <10 4 125 1.18 4 3BAcceptable <10 5 125 1.16 3.8 2B Acceptable <10 6 — — — — — — 7 125 1.164 4B Excellent <10 8 125 1.17 4 4B Excellent <10 9 125 1.18 3.8 4BExcellent <10 10 — — — — — — 11 125 1.2 4 3B Poor <10 12 125 1.2 4 3BPoor <10 13 125 1.2 4 3B Acceptable <10 14 125 1.2 4 3B Acceptable >1015 125 1.2 3.8 2B Acceptable >10 16 125 1.23 3.2-3.5 1H-3H Excellent <10

It was observed that about 0.0005 to about 0.003, or more particularly,about 0.002 mole of TBAH resulted in an optimized rate of reaction.Lower amounts of TBAH slowed the rate of reaction, whereas, higheramounts increased the reaction rate to gel formation level.

It was determined that Examples 1-16 all had refractive indices near1.23 and percent transmission gains (over uncoated substrates) of up to4%. Pencil hardness results generally indicated an acceptable scratchresistance, with Example 16 having particularly high scratch resistance.Examples 3-5, 7-9 and 16 also exhibited acceptable to excellent coatingadhesion using the Adhesion Tape Test.

Example 11 was also modified to include 0.00015 mole ofdiethylphosphatoethyltriethoxy silane (while maintaining 1 mole totalmonomer), in the reaction solution. This improved hardness and adhesion,however, the refractive index of the coated film increased from 1.2 to1.3. Certain examples were also treated with a 50-50 mixture of ethanoland water before curing in order to remove TBAN (tetrabutyl ammoniumnitrate) that would otherwise be present on the film as a result ofreaction between the TBAH and the nitric acid. It was found that thiswashing step further improved the hardness of the films. In some cases ahardness of 3H could be achieved by this treatment prior to the curingstep.

Example 16 was further subjected to several durability tests as setforth in Table 3 below to determine whether adhesion or transmittancewas lost.

TABLE THREE Parameter Test Conditions Result Salt spray in salt (5%NaCl) chamber at 35° C. Pass test(DIN50021) for 96 h and then in DIwater rinse and air dry Climate variable test −40 to +85° C., 100 cyclePass (IEC1215) Damp test 130° C., 85% humidity, 96 h Pass (IEC61250)Boiling DI water test submerge in boiling water for 30 min Pass and thenrub coating with a paper soaked in n-propanol Abrasion resistance linearabraiser, 500 g weight, 500 Pass (ISO-9211-3-1-02) rubs UV stabilityexposed under UV light @ 254 nm Pass at room temperature for 1 h Acidtest (DIN50018) 0.67% sulfuric/sulfurous acid, 40° C. Pass 20 cycle of2.5 min each Base test same as acid test but with 0.67% aq. Pass NaOH

A “pass” indicated less than 0.02 loss of transmittance and nodetectable chance in adhesion. As shown above, Example 16 passed alldurability tests.

Samples of Example 16 was further tested to confirm stability afterapproximately ten days at room temperature. As shown in Table Fourbelow, coating solution samples were formed having varying molarconcentrations of polymer material.

TABLE FOUR Samples of Example 16 Item 2% 3% 4% 16% Comments (condition:RT) Density(g/ml) 0.814 0.814 0.815 0.819 Weight 20 ml solution Solid0.81 1.25 1.72 6.68 ASTM D1644, 150 C. 30 content(%) min Viscosity(cP)0.76 0.80 0.83 1.81 ASTM D446, Cannon- Fenske viscometer tube PH value~4 ~4 ~4 ~3 PH test paper

The results shown in Table 4, indicate that the samples maintained aviscosity of less than 2.0 cP and a pH of about 3-4 after storage, whichconfirmed stability of the coating solution.

EXAMPLES 17-42

Tables 5-6 provide composition and performance data for Examples 17-42,in which different types and amounts of one or more adhesion promotingmaterials were added. In Examples 17-40, 122 grams of isopropanol and 62grams of acetone were charged into a reactor. In Examples 41-42, 366grams of isopropanol and 250 grams of acetone were charged in a reactor.

In each example, tetraethoxy silane (TEOS) and/or methyltriethoxy silane(MTEOS) were added to the reactor while stirring with an agitator. Atleast one of VTEOS, DMDEOS, MDEOS and/or TIPO was also added.

In Examples 17-40, TBAH (0.002 moles of 40% aq. solution) was used asthe base. In Examples 41 and 42, 0.006 moles of TBAH was added as a basecatalyst, and additional water was also added.

The reaction mixture was then heated to 35-70° C. for 3.5 h. Thereaction mixture was then cooled to 45° C. and nitric acid was added tothe reaction mixture in a semi-batch fashion to adjust the pH of thereaction mixture to 0.5-1.7. The reaction mixture was then cooled anddiluted with IPA, Acetone, PGMEA, and/or water. In Examples 41 and 42,the reaction mixture was diluted with a combination of 14 weight percentPGMEA, 46.472 weight percent IPA, 37.38 weight percent acetone and 1.87weight percent water.

After dilution and pH control the polymer formulation was stored in a−20° C. to −40° C. freezer. The molecular weight was measured by GPC andit was around 25,000-150,000 Dalton depending on reaction conditions.

These formulations were then deposited on glass substrates by spincoating. In almost all cases the desired coating thicknesses of 125 nmwas obtained after cure at 200-700° C., more favorably at 600-750° C.,in air or nitrogen after 3 minutes to 1 hour.

The same tests performed on Examples 1-16 were performed on Examples17-40 and are set forth in Table 6. Examples 41 and 42 included slightlydifferent tests, including average light transmission gain from 350 to1200 nm and a Surface Roughness (RMS) Test, as set forth in Table 7,which was measured by scanning force microscopy. The Scratch Test wasmeasured pursuant to EN-1096-2.

TABLE FIVE TEOS MTEOS DMDEOS MDEOS Water VTEOS TIPO Example (moles)(moles) (moles) (moles) (moles) (moles) (moles) 17 0.095 0 0.005 0 0 0 018 0.09 0 0.01 0 0 0 0 19 0.085 0 0.015 0 0 0 0 20 0.08 0 0.02 0 0 0 021 0.089 0.01 0 0.001 0 0 0 22 0.088 0.01 0 0.002 0 0 0 23 0.087 0.01 00.003 0 0 0 24 0.086 0.01 0 0.004 0 0 0 25 0.085 0.01 0 0.005 0 0 0 260.087 0.005 0.005 0.003 0 0 0 27 0.0885 0.01 0 0 0 0.0015 0 28 0.0870.01 0 0 0 0.003 0 29 0.0855 0.01 0 0 0 0.0045 0 30 0.085 0.01 0 0 00.005 0 31 0.0891 0.01 0 0 0 0.0009 0 32 0.089 0.01 0 0 0 0.001 0 330.0899 0.01 0 0 0 0 0.0001 34 0.0897 0.01 0 0 0 0 0.0003 35 0.0895 0.010 0 0 0 0.0005 36 0.088 0.01 0 0 0 0 0.0002 37 0.087 0.01 0 0 0 0 0.000338 0.087 0.01 0 0.0015 0 0.0015 0 39 0.084 0.01 0 0.003 0 0.0003 0 400.0865 0.005 0.005 0.0015 0 0.0015 0.0005 41 0.37 0.21 0 0 0.712 0.006 042 0.37 0.21 0 0 0.712 0.006 0.001

TABLE SIX RI at % T Pencil Adhesion Thickness 550 Gain at Hard- TapeContact Example (nm) nm 550 nm ness Test Angle 17 125 1.18 4 6BAcceptable <10 18 125 1.18 4 6B Acceptable <10 19 125 1.18 4 6BAcceptable <10 20 125 1.18 4 6B Acceptable >10 21 125 1.19 4 HBExcellent <10 22 125 1.19 4 HB Excellent <10 23 125 1.19 4 HB Excellent<10 24 125 1.19 3.8 HB Excellent <10 25 125 1.19 3.6 HB Excellent <10 26125 1.18 4 HB Excellent <10 27 125 1.21 4 H Excellent <10 28 125 1.21 4H Excellent >10 29 125 1.21 3.8 H Excellent <10 30 125 1.22 3.6 HExcellent <10 31 125 1.23 3.5 2H Excellent >10 32 125 1.24 2.9 2HExcellent >10 33 125 1.25 4 H Excellent <10 34 125 1.2 4 H Excellent <1035 125 1.2 3.8 H Excellent >10 36 125 1.2 2.9 H Poor >10 37 125 1.2 3.5H Poor >10 38 125 1.21 4 2H Excellent >10 39 125 1.24 3.6 3HExcellent >10 40 125 1.25 3.5 3H Excellent >10

TABLE SEVEN Average % Surface Thickness T Gain Scratch AdhesionRoughness Example (nm) (350-1200 nm) Test Tape Test (RMS) 41 125 3.1pass pass <1 Å 42 125 3.0 pass pass <1 Å

Examples 17-42 indicate that the addition of VTEOS, DMDEOS, MDEOS andTIPO improved certain physical characteristics of the AR coatings,including scratch resistance/hardness and/or adhesion. VTEOS, inparticular, appeared to improve film hardness and uniformity.

It was also determined that the reactions described herein can be scaledup to 100 to 1000 liter batch sizes without difficulty or losses in theresulting optical and mechanical properties of the resulting film.

Various modifications and additions can be made to the exemplaryembodiments discussed without departing from the scope of the presentinvention. For example, while the embodiments described above refer toparticular features, the scope of this invention also includesembodiments having different combinations of features and embodimentsthat do not include all of the described features. Accordingly, thescope of the present invention is intended to embrace all suchalternatives, modifications, and variations as fall within the scope ofthe claims, together with all equivalents thereof.

The invention claimed is:
 1. An anti-reflective coating compositioncomprising: a liquid medium comprising a majority amount of organicsolvent; polymer particles dispersed in the liquid medium, the polymerparticles comprising: at least one tetraalkoxy silane residue includinga silicon atom bonded to four oxygen atoms; and at least one secondalkoxy silane residue including a silicon atom bonded to at least onecarbon atom, the at least one second alkoxy silane residue selected fromthe group consisting of trialkoxy silanes, dialkoxy silanes, monoalkoxysilanes, and combinations thereof, wherein the polymer particlescomprise 35 to 50 mole percent of the at least one second alkoxy silaneresidue based on the total moles of polymer particles and wherein thepolymer particles have an average particle size of less than 10 nm; andthe coating composition having a pH of no more than
 5. 2. Theanti-reflective coating composition of claim 1 wherein the polymerparticles consist essentially of tetraethoxy silane residues andmethyltriethoxy silane residues.
 3. The anti-reflective coatingcomposition of claim 1 wherein the coating composition has a viscosityof no more than 2.0 cP.
 4. The anti-reflective coating composition ofclaim 1 wherein the at least one tetraalkoxy silane residue comprisestetraethoxy silane.
 5. The anti-reflective coating composition of claim1 wherein the at least one tetraalkoxy silane residue comprisestetraethoxy silane and the second alkoxy silane comprisesmethyltriethoxy silane.
 6. The anti-reflective coating composition ofclaim 1 wherein the at least one second alkoxy silane comprises avinyltriethoxy silane.
 7. The anti-reflective coating composition ofclaim 1 wherein the polymer particles consist essentially of tetraethoxysilane residues and methyltriethoxy silane residues and have an averageparticle size of less than 1 nm.
 8. The anti-reflective coatingcomposition of claim 1 wherein the polymer particles have an averageparticle size of less than 1 nm.
 9. The anti-reflective coatingcomposition of claim 1 wherein the polymer particles have an averageparticle size between 1 nm and 10 nm.
 10. An anti-reflective coatingcomposition comprising: a solvent; and polymer particles comprising: atleast one tetraalkoxy silane residue including a silicon atom bonded tofour oxygen atoms; and at least one second alkoxy silane residueincluding a silicon atom bonded to at least one carbon atom, the atleast one second alkoxy silane residue selected from the groupconsisting of trialkoxy silanes, dialkoxy silanes, monoalkoxy silanes,and combinations thereof, wherein the polymer particles comprise 35 to50 mole percent of the at least one second alkoxy silane residue basedon the total moles of polymer particles, the polymer particles having anaverage particle size of less than 1 nm.
 11. The anti-reflective coatingcomposition of claim 10 wherein the polymer particles consistessentially of tetraethoxy silane residues and methyltriethoxy silaneresidues.
 12. The anti-reflective coating composition of claim 10wherein the coating composition has a viscosity of no more than 2.0 cP.13. The anti-reflective coating composition of claim 10 wherein thecoating composition has a pH of no more than 5.0.
 14. Theanti-reflective coating composition of claim 10 wherein the at least onetetraalkoxy silane residue comprises tetraethoxy silane.
 15. Theanti-reflective coating composition of claim 10 wherein the at least onetetraalkoxy silane residue comprises tetraethoxy silane and the secondalkoxy silane comprises methyltriethoxy silane.
 16. The anti-reflectivecoating composition of claim 10 wherein the at least one second alkoxysilane comprises a vinyltriethoxy silane.
 17. An anti-reflective coatingcomposition comprising: a liquid medium comprising a majority amount oforganic solvent; polymer particles dispersed in the liquid medium, thepolymer particles comprising: at least one tetraalkoxy silane residueincluding a silicon atom bonded to four oxygen atoms; and at least onesecond alkoxy silane residue including a silicon atom bonded to at leastone carbon atom, the at least one second alkoxy silane residue selectedfrom the group consisting of trialkoxy silanes, dialkoxy silanes,monoalkoxy silanes, and combinations thereof, wherein the polymerparticles comprises 35 to 50 mole percent of the at least one secondalkoxy silane residue based on the total moles of polymer particles, thepolymer particles having an average particle size of less than 1 nm; andthe coating composition having a pH of no more than
 5. 18. Theanti-reflective coating composition of claim 17 wherein the at least onetetraalkoxy silane residue comprises tetraethoxy silane.
 19. Theanti-reflective coating composition of claim 17 wherein the at least onetetraalkoxy silane residue comprises tetraethoxy silane and the secondalkoxy silane comprises methyltriethoxy silane.
 20. The anti-reflectivecoating composition of claim 17 wherein the coating solution compositionhas a viscosity of no more than 2.0 cP.